This invention relates to sorting apparatus. It is particularly concerned with such apparatus which grades a stream of product in free flight according to colour characteristics, and activates an ejection mechanism based on that grading to remove selected product from the stream. The present invention is directed at a delivery system for creating the product stream in a form suitable for grading and sorting in this manner.
Product in free flight can be effectively graded using a variety of optical techniques. A basic technique is essentially monochromatic and classifies light reflected from product pieces as "dark" or "light". If the amount of "dark" exceeds a given threshold for a particular piece, then that piece is rejected. More sophisticated techniques monitor reflected light in different colours. Various sorting apparatus which grade product according to its ability to reflect light in different wavelength ranges are described in U.S. Pat. Nos. 4,203,522; 4,513,868; 4,699,273; and 5,538,142, the disclosures of which are incorporated herein by reference. In apparatus disclosed in the '522 and '142 Patents for example, detectors are responsive to light reflected from a product in different wavelength ranges, and generate signals indicative of different qualities of the product These signals are compared and analyzed, to generate a signal which can activate an ejector to remove the relevant item from the product stream.
In sorting apparatus of the kind described above it is of course important that the product stream is created in a form which enables items therein to be accurately graded and identified for ejection if appropriate. Normally, this stream is created by discharge from a chute, or from a horizontal or nearly horizontal conveyor driven at an appropriate speed. A chute is appropriate where the product to be graded is of generally consistent size and shape such as peas, coffee beans and rice. However, the relative movement between product and chute can generate static friction forces in the product which adversely affect the stream discharged therefrom, and any moisture in the product can also disrupt the uniformity of the flow. A conveyor system is normally preferred where product pieces of more widely varying size and moisture content are to be included in the stream, and the conveyor provides for the product to be stabilized on the belt before discharge into free flight. However, horizontal conveyors of the kind required to achieve the requisite stability in product moving at speeds of around 3 meters per second on the conveyor require a considerable space in which to operate effectively. Further, even at 3 meters per second, product can adhere to the conveyor at the point of discharge resulting in product not being discharged with a consistent trajectory, and thus not being properly graded. Additionally, the trajectory of the product stream from the conveyor means that an optical grading system will normally have components disposed above and below it, with the consequence that unwanted material in the stream can fall onto such components, resulting in improper functioning and inaccurate sorting.